CONSTRUCTION AND VALIDATION OF IN VITRO DOSE-RESPONSE CALIBRATION CURVE USING DICENTRIC CHROMOSOME ABERRATION

Dose-response curve for induction of unstable chromosome aberrations by 6 MV linear accelerator photons: Analysis of intra-experimental variations

Cytogenetic biodosimetry relies on dose-response curves (DRCs) for each type of radiation that can cause a radiation emergency. We have constructed a DRC based on the dicentric assay. Blood samples from four healthy volunteers were irradiated with acute 6 MV linac photons, 0.46-4.55 Gy; 0.68 and 1.37 Gy doses were used in the 'blind' validation study. Lymphocytes were cultured with variations in time delay in mitogenic stimulation after irradiation (2 vs. 16 h) and mitotic arrest by colchicine (3.5 vs. 16 h). Aberrations were scored in the first division metaphases, ensured by fluorescence-plus-Giemsa staining. DRCs for dicentrics and dicentrics plus centric rings were efficiently fitted using the linear-quadratic model. We show, for the first time, that neither prolonged mitotic arrest nor delayed mitogenic stimulation has any effect on DRC. However, the latter factor caused a significant increase in the yield of the second division metaphase in culture. Inter-donor differences in the DRC for aberrations were not large, but individual changes in the frequencies of second-division cells were highly variable. In the validation study, the DRC combined from all experimental series provided dose estimates that were as accurate as those, obtained using the donors' individual or culture-type specific DRCs. The DRC coefficients in present study were slightly higher than those reported previously for linac beams and close to values for orthovoltage X-rays. Further cytogenetic studies of megavoltage radiation beams require stringent standardization of experimental conditions.

Dicentric chromosome assay using a deep learning-based automated system

The dicentric chromosome assay is the "gold standard" in biodosimetry for estimating radiation exposure. However, its large-scale deployment is limited owing to its time-consuming nature and requirement for expert reviewers. Therefore, a recently developed automated system was evaluated for the dicentric chromosome assay. A previously constructed deep learning-based automatic dose-estimation system (DLADES) was used to construct dose curves and calculate estimated doses. Blood samples from two donors were exposed to cobalt-60 gamma rays (0-4 Gy, 0.8 Gy/min). The DLADES efficiently identified monocentric and dicentric chromosomes but showed impaired recognition of complete cells with 46 chromosomes. We estimated the chromosome number of each "Accepted" sample in the DLADES and sorted similar-quality images by removing outliers using the 1.5IQR method. Eleven of the 12 data points followed Poisson distribution. Blind samples were prepared for each dose to verify the accuracy of the estimated dose generated by the curve. The estimated dose was calculated using Merkle's method. The actual dose for each sample was within the 95% confidence limits of the estimated dose. Sorting similar-quality images using chromosome numbers is crucial for the automated dicentric chromosome assay. We successfully constructed a dose-response curve and determined the estimated dose using the DLADES.

ESTABLISHMENT OF THE IN VITRO DOSE-RESPONSE CALIBRATION CURVE FOR X-RAY-INDUCED MICRONUCLEI IN HUMAN LYMPHOCYTES

The cytokinesis-block micronucleus assay has proven to be a reliable technique for biological dosimetry. This study aimed to establish the dose-response curve for X-ray-induced micronucleus. Peripheral blood samples from three healthy donors were irradiated with various doses and scoring criteria by the micronuclei (MN) in binucleated cells. The results showed that the frequency of MN increased with the elevation of radiation dose. CABAS and Dose Estimate software were used to fit the MN and dose into a linear quadratic model, and the results were compared. The linear and quadratic coefficients obtained by the two software were basically the same and were comparable with published curves of similar radiation quality and dose rates by other studies. The dose-response curve established in this study can be used as an alternative method for in vitro dose reconstruction and provides a reliable tool for biological dosimetry in accidental or occupational radiation exposures.